Preheat your oven to 350°F (175°C).
In a large skillet, heat the olive oil over medium heat. Add the diced onion and bell pepper, and sauté for about 5 minutes until they are softened.
Add the minced garlic and cook for an additional minute until fragrant.
Add the Italian sausage to the skillet, breaking it up with a spoon. Cook until browned and cooked through, about 7-10 minutes. Drain any excess fat.
Stir in the diced tomatoes (with their juice), cooked rice, Italian seasoning, salt, and pepper. Mix well to combine all ingredients.
Remove the skillet from heat and stir in half of the cheddar and mozzarella cheese.
Transfer the mixture to a greased 9x13 inch baking dish. Top with the remaining cheese.
Bake in the preheated oven for 20-25 minutes, or until the cheese is bubbly and golden.
Remove from the oven and let it cool for a few minutes. Garnish with chopped parsley if desired before serving.